Antarctic ice breakup makes ocean absorb more CO2

Opinion Some cheerful news on the climate change front today, as US government boffins report that ice breaking off the Antarctic shelves and melting in the sea causes carbon dioxide to be removed from the environment. This powerful, previously unknown "negative feedback" would seem likely to revise forecasts of future global warming significantly downwards.

The US National Science Foundation (NSF) which funded the iceberg study, describes the results as having "global implications for climate research".

A team of NSF-funded scientists examined the effects on an area of the Weddell Sea of a large (20 mile long) berg moving through, melting as it went and diluting the salty sea water - also adding key nutrients carried from the land. They found that after the iceberg had passed, levels of CO2 had plunged and much more chlorophyll was present. Chlorophyll is the substance in green plants which lets them suck in nasty CO2 and emit precious life-giving oxygen: in the Weddell Sea it was present in phytoplankton, tiny seagoing plantoids which are thought to account for half the carbon removed from the atmosphere globally.

The scientists say that more and more icebergs are set to be found in the seas around the Anatarctic as more ice breaks off the shelves attached to the peninsula which reaches up from the polar continent towards South America. This should mean more phytoplankton and thus less CO2.

The iceberg team consider that the increased number of bergs coming from the western Antarctic is the result of warming temperatures in the region, though recent research from British boffins has suggested that in fact other factors may be in play - at least in the case of the Pine Island Glacier, one of the major sources of sea ice in that area.

If the phytoplankton-boosting effect of the bergs is as big as the NSF appears to be suggesting, however, it would seem that any carbon-driven temperature rise could be at least partly self-correcting.

Increased iceberg shedding would seem likely to be seen mainly or only around the western peninsula: antarctic sea ice shelves elsewhere are actually growing, not shrinking, and at such a rate as to outweigh the peninsular losses. The past three decades have seen the south-polar ice sheets grow by 300,000 square kilometres overall.

The NSF study was originally published in the journal Deep Sea Research Part II (subscription required). It was flagged up more recently in Nature Geoscience's top picks (again, subscription link). The NSF also has a statement here. ®